Tuberculosis (TB) is an infectious disease that affects mainly the lungs (pulmonary TB). A person with pulmonary TB is infectious to others, without treatment this person may infect 10-15 persons/year.
TB is closely connected with HIV. People living with HIV are about 37 times more likely to develop TB than HIV negative people. In 2009, TB accounted for 25% of deaths among HIV-positive people. Developing countries especially with high HIV prevalence are the high burden TB areas.
More than 90% of people with drug-susceptible TB can be cured in six months using combinations of first-line drugs such as Rifampicin and Isoniazid. Inadequate treatment, low compliance or intermittent therapy may lead to development of resistance against the first line drugs. Sometimes even the primary infection occurs with resistant MTB bacteria.
The recommended treatment of new-onset pulmonary tuberculosis, as of 2010, is six months of a combination of antibiotics containing rifampicin, isoniazid, pyrazinamide, and ethambutol for the first two months, and only rifampicin and isoniazid for the last four months. Where resistance to isoniazid is high, ethambutol may be added for the last four months as an alternative. If multiple drug-resistant TB is detected, treatment with at least four effective antibiotics for 18 to 24 months is recommended.
Primary resistance occurs when a person becomes infected with a resistant strain of TB. A person with fully susceptible TB may develop secondary (acquired) resistance during therapy because of inadequate treatment, not taking the prescribed regimen appropriately (lack of compliance), or using low-quality medication. Drug-resistant TB is a serious public health issue in many developing countries, as its treatment is longer and requires more expensive drugs. MDR-TB is defined as resistance to the two most effective first-line TB drugs: rifampicin and isoniazid. Extensively drug-resistant TB is also resistant to three or more of the six classes of second-line drugs. Totally drug-resistant TB is resistant to all currently used drugs. It was first observed in 2003 in Italy, but not widely reported until 2012 and has also been found in Iran and India.
Treatment of MDR-TB with second line drugs is more challenging, more costly, causes more severe side effects, and must be taken for up to two years. Cure rates for MDR-TB are lower, typically ranging from around 50% to 70%.
It is important to identify patients with TB resistant bacteria to start immediate treatment and reduce the spread of the resistant MTB.